1. Field of the Invention
This invention relates to an optical disc apparatus for reading and reproducing data recorded on an optical disc such as a CD or a DVD.
2. Description of the Related Art
Conventionally, in an optical disc apparatus for reading data recorded on an optical disc such as a CD or a DVD, focus control for matching a focusing position of applied laser light with a record surface of the optical disc has been performed. This focus control is control in which an objective lens arranged between the optical disc and an LD which is a light source is moved in a direction of approaching to and receding from the optical disc. The LD, the objective lens, an actuator for moving this objective lens in the direction of approaching to and receding from the optical disc, etc. are disposed in a pickup head. A signal inputted to the actuator in the focus control is a signal in which a focus servo signal generated based on a focus error signal (hereinafter called FE signal) indicating the amount of deviation of the record surface of the optical disc from the focusing position of the applied laser light is superimposed on a focus bias as is publicly known.
This focus bias is adjusted to a voltage in which amplitude of an RF signal which is a reading signal of data recorded on the optical disc is maximized. In other words, the optical disc apparatus is provided with a configuration for adjusting the focus bias so as to maximize the amplitude of the RF signal. This focus bias adjustment includes, for example, a method for stepwise changing a focus bias and sampling an RF signal and adjusting the focus bias to a voltage in which amplitude of the RF signal is maximized (see JP-A-2002-312959). Also, a method for adjusting a focus bias so as to minimize the amount of jitter of an RF signal (see JP-A-2002-100056) has been proposed.
Also, in JP-A-2002-100056, the method in which at the time of adjusting a focus bias, for a period during which jitter extremely increases because of flaws in an optical disc or dirt etc. adhering to the optical disc, information obtained for its period is not used for adjustment of the focus bias and thereby adjustment accuracy of the focus bias is prevented from reducing has been proposed.
However, in the method for stepwise changing a focus bias and sampling an RF signal and adjusting the focus bias to a voltage in which amplitude of the RF signal is maximized, the method for preventing a reduction in adjustment accuracy of the focus bias because of flaws in an optical disc or dirt etc. adhering to the optical disc has not been proposed yet. In other words, in the method for stepwise changing the focus bias and sampling the RF signal and adjusting the focus bias to the voltage in which amplitude of the RF signal is maximized, there was a problem that the adjustment accuracy of the focus bias reduces because of flaws in the optical disc or dirt etc. adhering to the optical disc.